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[en] The motional behaviour of hexadecane-h34 within the pseudo-hexagonal channels provided by the urea-d4 framework has been studied by incoherent quasielastic scattering between 5 K and 370 K. On the instrument time scale (80 μeV), at least two components could be separated, which are attributed to reorientational jumps of the paraffins around their long axes and damped librations, respectively. At 147 K a phase transition takes place involving an orthorhombic deformation of the host channels and a simultaneous change of 60 degrees to 180 degrees jumps. From the activation energy it is concluded that the motional properties of the included molecules are responsible for this transition. (author) 6 refs., 4 figs
[en] Highlights: • Standard enthalpies of formation of nitrogen-containing compounds were calculated. • Isodesmic reactions at the CCSD(F12∗)(T) level were used for ureas and s-triazines. • HEAT protocols were applied to methanimine and methylamine. • Good agreement with experimental data, where available, was achieved. Gas-phase standard enthalpies of formation of selected ureas and s-triazines were calculated at the CCSD(F12∗)(T)/cc-pVTZ-F12//ωB97X-D/cc-pVTZ level of theory by employing isodesmic reactions. The following values were obtained (T = 298.15 K, units: kJ mol−1, estimated confidence interval 95%): urea, −231.9 ± 2.8; biuret, −430.0 ± 4.5; triuret, −620.3 ± 6.3; cyanuric acid, −451.6 ± 6.3; ammelide, −303.9 ± 6.4; ammeline, −106.5 ± 6.2; melamine, 70.1 ± 7.0. The standard enthalpies of formation of methanimine and methylamine, which were required for the isodesmic reactions, were calculated from atomization reactions by using several variants of the HEAT approach. The following results were considered most reliable (T = 298.15 K, units: kJ mol−1, estimated confidence interval 95%): methanimine, 89.0 ± 1.0; methylamine, −20.7 ± 1.0.
[en] The liquid wastes generated by the reprocessing of spent fuel can be converted into solid form by using several known processes. When the wastes contain nitrates and nitrites large quantities of noxious nitrogen oxide gases are formed, which are at present released to the atmosphere. Their evolution may be suppressed by adding urea to the waste solution before the solution is heated, so that upon heating the urea reacts wth the nitrates and nitrites to evolve elemental nitrogen, carbon dioxide and ammonia. The addition of urea does not add any additional materials to the solids being formed from the waste solution. A slight excess of a stoichiometric amount of urea relative to the nitrates and nitrites present is added to the liquid waste, and the solution is heated to at least 1300 C while bubbling carbon dioxide through the solution. This method can be used with the pot calcination process of waste solidification, or in the fluidized bed calcination process. (LL)
[en] In the present work, impingement behaviour of an aqueous urea solution is investigated experimentally. The effects of droplet diameter, impact velocity and substrate temperature are evaluated by monitoring single droplet impingement with a high-speed camera. Results allow the formulation of four different interaction regimes and a regime map depending on hydrodynamic and thermal parameters is proposed. The regimes deposition, splash, boiling-induced breakup, rebound with breakup and the transition boundaries are discussed in detail. Results show that the solute significantly affects the outcome of droplet impingement promoting droplet disintegration by enhanced nucleation and bubble formation. Comparison with literature data reveal the strong dependency of droplet impact behavior on the Weber number as a combination of initial droplet diameter and impact velocity.
[en] Obesity in nontransplant patients has been associated with hypertension, hyperlipidemia, diabetes, and proteinuria. To determine whether renal transplant recipients with an elevated BMI have worse long term graft survival, we prospectively studied 92 patients transplanted between April 1999 and July 2000. Weight (Wt) and height of the patients were recorded prior to transplantation and two weeks, one, two and three years post transplantation. Blood urea nitrogen (BUN), creatinine (Cr) and blood pressure were checked monthly, while triglyceride, cholesterol, high density lipoprotein (HDL), and low density lipoprotein (LDL) were obtained 3 monthly for 3 years post transplantation. Graft dysfunction was defined as serum Cr > 1.8 mg/dL. While BMI and Wt of the patients before transplantation did not show any significant correlation with chronic renal allograft dysfunction (CRAD), patients with higher Wt and BMI two weeks after transplantation showed an increased risk of developing CRAD during the three year post transplant independent of other risk factors (P< 0.05). Patients with greater Wt loss in the first two weeks post transplantation showed a decreased risk of developing CRAD in the following 3 years (P< 0.001). Our study suggests that high Wt and BMI are significantly associated with worse graft survival 3 years post renal transplantation. (author)
[en] Understanding the speciation and kinetics of metal ions in heterogeneous hydrogen bonded deep eutectic solvents (DES) has immense importance for their wide range of applications in green technology, environmental remediation and nuclear industry. Unfortunately, the fundamental nature of the interaction between DES and actinide ions is almost completely unknown. In the present work, electrochemical investigations of uranyl ion (UO22+) in DES (Reline) consisting of choline chloride (ChCl) as hydrogen-bond acceptor and urea as the hydrogen-bond donor, has been initiated
[en] A technique has been developed to enable urea formaldehyde resins to be located in particle boards using Energy Dispersive Analysis of X-rays (EDAX). This method of detection requires the resin to be chemically labelled, and several possible chemicals are proposed. The merits of each of these chemicals are discussed and thiourea and chloral are selected as the best potential labels. It is necessary to ensure that adding these chemicals to a resin will not alter the resin's properties. For this reason the thiourea and chloral labelled resins' physical properties are compared with those of an unlabelled resin. The effect of cyclic soaking (in water) and drying on the physical behaviour and tensile strengths of labelled and unlabelled resin films is also assessed. As a result of these, and later experiments, chloral is rejected as a suitable label. All subsequent investigations of resin microdistribution are carried out using a thiourea/urea formaldehyde resin. These studies reveal several important characteristics of particleboard ''glue lines''. The majority of resin is concentrated close to the ''glue line'' and is rarely found more than two cells away from the chip junction. Little or no resin is observed in the cell lumen, but there is evidence of cell wall penetration and possible within cell wall distributions are identified. Finally the implications of the cycling, tensile strength and resin distribution data are discussed with reference to the problems of particleboard failure in moist environments. (author)
[en] Twenty-nine strains of Coprinus species comprising 16 strains from 12 identified species and 13 unidentified strains as well as one Arthromyces ramosus strain were screened for the production of extracellular peroxidase. Among the fungi examined, three strains of C. cinereus, UAMH 4103, UAMH 7907 and IFO 30116, as well as one Coprinus sp., UAMH 10067, which was isolated from urea treated soil, were shown to produce large amounts of extracellular peroxidase. The performance of crude peroxidase, obtained from liquid culture of C. cinereus, (CIP) on phenol removal from synthetic wastewater was evaluated and compared with that of purified horseradish peroxidase and A. ramosus peroxidase. Although crude CIP performed better than both purified enzymes, its superiority vanished in the presence of poly(ethylene glycol), a known protective agent of peroxidase. This suggests that the residual soluble substances present in crude CIP have protective effects similar to those of poly(ethylene glycol). (author)
[en] Complete text of publication follows. In this paper the influence of halloysite structure on the properties of melt-prepared polymer nanocomposites have been studied. Intercalation of halloysite (HLS) carried out in solution as well as by dry mechanochemical method has been investigated by vibrational spectroscopic techniques. Except of currently used modifiers (alkylamines, silanes), an intensive study of organo-clay nanocomplexes (with potassium-acetate, urea, formamide and acetamide) has been investigated and new structural models (as well as reaction pathways) were proposed. It was found that modification of halloysite by alkylamines as well as silanes did not lead to intercalated structure of halloysite. Mechanochemical treatment with urea, however, resulted in an intensive intercalation of halloysite. Surface activation of the mineral has been achieved by the thermal treatment of the complex. The impact of the intercalated structure of halloysite was confirmed by improving mechanical properties, as well as by reduction of flammability of PP/halloysite nanocomposites. The investigation of the structure of polymer nanocomposites based on intercalated halloysite confirmed considerable reduction of particle size and high degree of filler exfoliation. The achieved results confirmed that there is a potential for future utilisation of natural halloysites for production of exfoliated polymer nanocomposites with outstanding end use properties.